1. Field of the Invention
The present invention relates to an optical transceiver that protects the internal bus in the host system from the miss-operation at the plugging of the transceiver in the host system.
2. Related Prior Art
A pluggable optical transceiver able to be plugged in the host system without turning off the power of the host system has been developed and has been commercially applied in the optical communication system. A multi-source agreement (MSA) distributed from the SFP committee through the internet, INF-8074i Specification for SFP transceiver, rev. 1,0, May 12, 2002, (ftp://ftp.seagate.com/sff/INF-8074.pdf) has been ruled specification of an optical transceiver called as SFP (Small Form-factor Pluggable) transceiver. The SFP transceiver implements a control unit that communicates with the primary control circuit of the host system via the command line when the SFP transceiver is plugged with the host system.
The input terminal of the control unit in the transceiver, which is connected with the command line, possibly receives an over-voltage on the command line. In order to protect the control unit of the transceiver, the command line may provide a protection circuit that includes a diode reversely connected with the power supply line of the transceiver and another diode reversely connected with the ground. These two diodes may limit the voltage level of the command line substantially between the power supply and the ground.
When the power supply in the transceiver is provided through the circuit that delays the supply of the power from the plugging of the transceiver with the host system, one of the protection diode connected to the power supply of the transceiver is forwardly biased during the delay of the power supply. Then the bus line within the host system that is just connected with the command line of the transceiver by plugging it with the host system probably causes an error. Specifically, while a unit connected with the bus line of the host system outputs a “H” level data, the practical data on the bus line becomes a “L” level because this bus line is connected with the command line of the transceiver and the command line is connected to the substantially ground level with the forwardly biased diode.
Whereas, the invention disclosed hereinbelow is to provide an optical transceiver by which the bus line within the host system is unaffected just after the plugging of the transceiver with the host system even when the transceiver provides an internal power supply circuit that delays the supply of the electric power to the internal unit of the transceiver.